Miniaturized circuit-breaker switch

ABSTRACT

A single-pole circuit-breaker switch for manual operation and free tripping comprising an insulating casing containing two stationary contacts and having a hand-operated closure pushbutton slidably fitted within the said casing and projecting therefrom, the said switch comprising means for retaining the said push-button in the depressed position, a frame which is movable within the casing and carries on the one hand two movable contacts which are capable of cooperating with the stationary contacts and are connected to each other by means of a U-shaped thermostatic element which has two arms connected to the movable contacts and the deformation of which causes tripping of the switch involving return of the sliding frame and push-button to the opening position and on the other hand locking means and means for releasing the movable frame under the action of the thermostatic element, connecting means pivotally attached to the push-button and to the movable frame and elastic restoring means for returning the movable portions to the opening position at the time of operation of the releasing means.

United States Patent [151 3,686,602 Aug. 22, 1972 l 3,456,225 7/ 1969 Ellenberger ..337/66 X Primary Examiner-J. V. Truhe Assistant Examiner-Gale R. Peterson Attorney-Holman & Stern [5 ABSTRACT A single-pole circuit-breaker switch for manual operation andfree tripping comprising an insulating casing containing two stationary contacts and having a handoperated closure push-button slidably fitted within the said casing and projecting therefrom, the said switch comprising means for retaining the said push-button in the depressed position, a frame which is movable within the casing and carries on the one hand two movable contacts which are capable of cooperating with the stationary contacts and are connected to each other by means of a U-shaped thermostatic element which has two arms connected to the movable contacts and the deformation of which causes tripping of the switch involving return of the sliding frame and v push-button to the opening position and on the other hand locking means and means for releasing the movable frame under the action of the thermostatic element, connecting means pivotally attached to the push-button and to the movable frame and elastic restoring means for returning the movable portions to the opening position at the time of operation. of the releasing means.

3 Claims, 6 Drawing Figures Patented ,Aug. 22,1972 3,686,602

5 Sheets-Shee t 1 Patented Aug. 22,1972

5 Sheets-Sheet 2 Patented Aug. 22,. 1972 3,686,602

5 Sheets-Sheet 5 5 Sheets-Sheet 4 Patented Aug. 22, 1-972 3,686,602

5 Sheets-Sheet 5 MlNlATURlZED CIRCUIT-BREAKER SWITCH This invention is directed to a single-pole circuitbreaker switch of small overall size which is intended to be actuated by hand as a push-pull" switch and is designed on the free-tripping principle.

A free-tripping device is understood to designate a device which is capable of opening its circuit in the presence of an overload current even in the event that the control means are maintained in the closed position for any indeterminate reason.

In order to comply with specifications in the aeronautical field which is primarily contemplated by the present invention, provision must be made. for 4 further technical characteristics and particularly the following:

snap-action tripping with instantaneous return of the control push-button which results in the appearance of a band having a well-defined color;

tripping after a given time interval in respect of a given overload; I

insensitivity to impacts, vibrations, accelerations and decelerations.

In addition to these requirements, it is often necessary to add a device which provides compensation for ambient temperature; furthermore, in order thatthe calibration should not be impaired in the course of time, it is important to ensure that the means which are responsive to the overload current are capable of initiating a trip without having to apply anexcessive effort and that no action should beproduced on said means at the time of manual control operations. v

All these essential conditions coupled with the fact that the apparatus must be of small size make the problem difficult to solve, with the result that the design solutions which have been proposed up to the present time are relatively complex and all suffer from the same major imperfection.

' The complexity of known designs usually arises on g the one hand from the electric circuit which comprises auxiliary connections and on the other hand from the number of welding or riveting operations which are necessary in order to obtain the different constituent sub-assemblies. So far as concerns the major imperfection referred-to above, this arises from the fact that all the elastic forces which are necessary for operation of the switch have componentswhich are notnegligible and are added to each other, all said components being applied at the point of engagement so that if the bearing surface of said point is substantial, the means which are responsive to the overload current must produce an excessive effort in order to initiate a trip whereas, if the bearing surface is small, a trip is liable to occur accidentally under the action of shocks or vibrations.

The circuit-breaker switch in accordance with this invention comprises means responsive to the overload groove in the lower portion thereof; a movable frame constituted by two symmetrical right-angle brackets which are assembled by means of two spacer members and one of said members being provided with an internally threaded bore which is oriented in the axial direction, said assembly being guided 'vertically by means of a lug formed in the flange of eachright-angle bracket and housed within an axial groove formed in the corresponding half-casing; an operating arm formed of two superposed side-plates which are joined together at each'end by means of a cross-pin, the upper cross-pin which is engaged in the inclined groove of the blade being adapted to cooperate with a guide and a plate so that the arm aforesaid can be maintainedin the bottom position whilst the lower cross-pin (actuating pin) whose extremities are engaged in a double-slope groove formed in each cheek of the movable frame is capable according to the position occupied by said cross-pin in said groove. either of imparting the downward movement of the'arm to the frame or of permitting the upward movement of the frame together with the arm which is maintained in the bottom position; a latch which is pivotally mounted on a pin carried by the cheeks of the movable frame and provided on one side of said pin witha recess whose angular position governs the position of the actuatingpin; a trip lever pivotally mounted on a pin carried by the checks of the movable frame and provided with a nose in cooperating relation with the latch in order that said latch should be either capable or not capable of carrying out a pivotal movement according to the position of said nose and consequently of releasing or retaining the actuating pin; an insulating contact-holder for supporting two flexible S-shaped strips each adapted to carry at the lower end thereof a movable contact which is intended to cooperate with the corresponding stationary contact; a thermostatic element constituted by a U- shaped bimetallic strip which surrounds the movable frame and is connected to the upper extremity of each flexible strip so as to produce action by means of an insulating stud fixed at the center of its central arm on a heel which is formed on the trip lever; a cruciform assembly plate for guiding the lower portion of the movable frame and maintaining the insulating contactholder; an assembly providing compensation for ambient temperature, and calibration and comprising two bimetallic strips connected at one end thereof to the upper extremity of the corresponding flexible strip, two small insulating plates for providing a mechanical connection between the lower extremities of the bimetallic strips and finally a blade-spring and an adjusting screw for the purpose of calibratingthe apparatus; a spring for maintaining the trip lever on the thermostatic element; a compression spring housed within the guide sleeve in order to retumthe push-button and the actuating arm; a compression spring housed within the positioning unit and adapted to produce action on the v assembly plate in order to ensure the elastic return of the movable frame.

' The foregoing properties will be clearly brought out in the following description, reference being made to the accompanying drawings, in which:

FIG. 1 is a sectional view of the apparatus in the joint plane of'the casing;

FIG. 2 is a partial sectional view taken along line II- II of FIG. 1;

FIG. 3 is a sectional view taken along line IIIIII of FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a part-sectional view in elevation in the closed position, assuming that the front half-casing has been removed;

FIG. 6 is a sectional view which is similar to FIG. 1,

the constituent elements being shown in the position occupied on completion of the initial thermal trip stage.

As shown in these different figures, the circuitbreaker switch according to the invention comprises:

a casing of. molded insulating material formed of two identical hollowed-out components 1 which are assembled by means of rivets fitted within holes la.

a pair of terminals 2 each carrying a stationary contact 2a and engaged in grooves lb, 1c, said grooves being formed in the bottom portion of the half-casing and maintained at a distance from each other by means of a positioning member 3 of molded insulating material.

a guide sleeve 4 which is inserted in the top portion of the casing'and has a threaded portion so that the apparatus can be attached to a panel by means of a nut. Said sleeve is stationarily fixed in the axial direction by means of a metallic plate 5 which is in turn secured to the casing by means of four lugs 5a which are folded back and provided with drilled holes, said lugs being set in recesses 1d of the casing; in addition, said sleeve is stationarily fixed angularly by means of diametrically opposite flat portions 4a formed on the annular shoulder 4a (as also shown in FIG. 3). A groove 4b of small width permits a local reduction in thickness of the wall as well as the possibility of forming a projecting key 4c as a result of a punching operation.

a control push-button constituted by the assembly of three components 6, 7, 8 of molded insulating material, the colors of said components as given by way of example being red in the case of the pushbutton 6 proper, green in the case of the component 7, white in the case of the washer 8. The purpose of this difference in color is to provide a visual display of the state of operation of the apparatus. A groove 7a in which the key 4c is engaged serves to guide said push-button within the sleeve 4.

an operating blade 9 of cut-out sheet metal, the top portion of which is engaged in the component 7 and locked in position with respect to this latter by means of a locking-pin l0. Said blade is disposed vided at the lower end with an inclined groove 9a. a movable frame formed of two symmetrical rightangle brackets 11 which are constructed of bent FIG. 4) is fixed on the frame by means of two rivets 13c and has an axial channel 13a and an internally threaded bore 13b. The flange 11a (shown in FIG. 2) is provided with a lug 11b which is formed at the time of cutting-out and is intended to fit within an axial groove 1e of the corresponding half-casing in order to ensure vertical guiding;

the cheek lie is provided with a groove 1 1d having a double slope and a swan-necked zone 1 1e.

an operating arm formed of two superposed sideplates 14 within which the lower portion of the operating blade 9 is inserted and connected to the extremities of these latter by means of a cross-pin. The upper cross-pin or retaining pin 15 which passes through the inclined groove 9a isacted upon by a radial 'force component (which is directed towards the left-hand side in the drawings). when the control push-button 6 is depressed and each extremity of the lower crosspin or actuating pin 16 isengaged in a groove 11d having a double obliquity or slope.

a retaining-pin guide 17 formed of molded insulating material and a retaining plate 18 formed of cut-out sheet metal, these two components being juxtaposed beneath the guide sleeve 4 and suitably positioned within the casing by virtue of their octogonal shape. Looking in plan on FIG. 3, it is observed that said assembly has a central opening 17a, 18a which permitsthe passage of the operating blade and arm 9, 14 but does not permit the passage of the retaining cross-pin 15; there is also located on each side of said opening a skew section or ramp 17b which terminates in a recess 17c, 180 through which the retaining pin 15 is capable of passing. Four studs 17d serve to center the spring 19 which produces elastic restoring action on the control push-button 6, 7, 8; two grooves 7b which are formed in'the base of said push-button prevent this latter from coming into' abutment with the shouldered portions 17e of the guide 17 at the end of travel. I

alatch 20 of cut-out sheet metal which is pivotally mounted on a pin 21 carried by the cheeks of a trip lever 22 of cut-out sheet metal and pivotally mounted on a pin 23 which is carried by the checks of the movable frame and centered with respect to said checks by means of two washers 24.

Said lever is provided with a heel 22b which is ap plied under the action of a loop-spring 25 against an insulating stud 26. Said stud is rigidly fixed to athermostatic element 27 which, depending on the position in which it is located, determines the angular position of the retaining nose 22a which is then either in cooperating relation or not with the bearing nose 28a of the latch 20 (as shown in FIGS. 5 and 6).-

an insulating contact-holder 28 formed of a base member 28a which isen gaged within the swannecked zone 112 of the movable frame and of two side-plates 28b which are applied respectively against the external faces of the cheeks of the movable frame.

an assembly plate 29 of cut-out and folded sheet metal for holding the insulating contact-holder plate 28 in a stationary position. Said plate 29 is of cruciform design and is provided on the one hand with two projecting lugs 290 formed by cutting-out from the sheet metal and .adapted to engage respectively in the axial guiding grooves 1e of the casing and on the other handwith a pintle 30 for centering a spring 31 which I is housed axially within the positioning unit 3 and produces elastic restoring action on the movable frame (as shown in FIGS. 2and3).

two S-shaped flexible strips 32 which are respectively attached at the center of said strips to the sideplates 28b of the insulating contact-holder 28 by means of a rivet 33 (as shown in FIG. 5). The bottom extremity of each flexible strip is adapted to carry a movable contact-stud 32a which is located opposite to the corresponding stationary contactstud 2a. I

a thermostatic element 27 constituted by a U-shaped bimetallic strip which surrounds the movable frame, the extremities of said element being joined respectively to the upper extremities of the flexible strips 32 in order to constitute a direct electrical circuit.

an element which provides compensation for .am-

bient temperature constituted by two identical bimetallic strips 34 each having a double elbow. At one end, said bimetallic strips are each clamped at the points of assembly of thermostatic element and flexible strips by means of a rivet 35, for example. At the other end, said bimetallic strips are coupled mechanically by clamping between two small insulating plates'36, 37 which are both provided with a slight concavity in their bearing zones (as shown in FIG. 5) in order to permit the possibility of thermal deformation of said strips. As shown in FIG. 2, the upper insulating plate 36 is also provided with a shouldered portion 36a in order to maintain the strips in spaced relation.

a blade-spring 38 and an adjusting screw 39 for maintaining the compensating eler'nent elastically on the movable frame in a position corresponding to calibration. In fact, it is apparent that an axial displacement of the screw 39 causes either upward bending or downward deflection of the thermostatic element 27, thereby modifying the position of the trip lever 22; the same also applies when the ambient temperature varies, in which case the thermal deformation of the bimetallic strips 34 performs the same function as the displacement of the screw 39.

The foregoing description clearly brings out the ease with which an apparatus of this type can be assembled since practically all the components can be assembled outside the casing. Calibration is carried out on the one hand during assembly by optical control and on the other hand after assembly by means of a tool inserted through an orifice (not shown) which is formed in the casing and subsequently closed off. l

"The operation of the apparatus as hereinbefore described is as follows:

In the rest condition, the components are located in the position shown in FIG. 1, this condition being indicated by the control push-button which displays zones of different colors. I

When the control push-button is depressed, the retaining cross-pin 15 which is urged towards the Lefthand side by the radial force component arising from the inclination of the groove 9a accordingly reacts with the lateral ramps 17b, passes through the lateral recesses 17c, 18c, then slides beneath the retaining plate 18 and is prevented by this latter from returning upwards. At the same time, the actuating pin 16 begins to react with the retaining heel 20b of the latch 20 and causes the pivotal movement of this latter until its nose 20a is applied against the nose 22a of the triplever 22. While continuing to be retained by the heel 20b said actuating pin produces action on the movable frame 1 1 and imparts a downward movement to this latter. After interlocking, that is to say after the cross-pin 15 is retained by the plate 18 (as shown in FIG. 5), only the red zone 6 of the control push-button is visible and the current which is supplied via one of the terminals 2 flows successively, before passing out via the other terminal 2, through one or both flexible strips 32, the U- shapedbimetallic strip 27, the other flexible strip 32.

When the switch has thus been closed and if the control push-button is then pulled upwards, the retaining cross-pin 15 is in this case displaced towards the right by the radial force component so that, at a given moment, said cross-pin will be permitted to return through the. lateral recesses l7c-l8c; at this moment, the complete assembly will consequently return upwards abruptly under the action of the springs 19-31 as these latter are released.

If the current intensity increases and the switch is in the closed condition, the thermostatic element 27 which carries the insulating stud 26 moves upwards and the angular position of the trip Lever 22 changes. When this position is such that the nose 22a frees the nose 200, the latch pivots under the thrust of the actuating pin 16 which is freed from the retaining heel 20b, engages in the double-slope groove 11d while the frame 11 moves upwards abruptly under the action of the spring 31. It can readily be visualized from FIG. 6 in which the apparatus is shown at this precise moment that a trip would take place even if the control pushbutton had been maintained in the engaged position for any reason. Apart from this particular contingency, the second trip-out stage is carried out by virtue of the spring 19 which initiates the upward movement of the operating blade 9 and consequently has the effect of displacing the retaining cross-pin 15 towards the lateral recesses l7c-18c, thereby causing the elastic return of the control push-button and of the operating arm 9. At

' the end of travel, the actuating pin 16 produces action on the finger 20c, with the result that the nose 20a is replaced beneath the nose 22a, this condition being essential in order to pennit re-closure of the switch. However, it is worthy of mention that any attempt to reclose the switch will remain of no avail as long as the thermostatic element 27 has not cooled to a sufficient extent to permit the nose once again. Y

It will also be noted that, at the moment of tripping, the stationary contact 2a and movable contact 32a slide with respect to each other, the effect of this movement being to break micro-welds and to ensure selfcleaning of contacts. v

Finally, it will be noted that, in the closed position 22a to retain the nose a shown in FIG. 5, the couple which is transmitted to the latch 20 by the actuating pin 16 is converted to a simple frictional force at the point of engagement (point of reaction of the noses 20a-22a) and that this force can be overcome by a much smaller force by reason of the leverage which exists between the pivot-pin 23 and the heel 22b of the locking lever 22. It is apparent that the sensitivity can be very considerable and that only an impact could cause rotation of the lever 22 in the clockwise direction and result in an accidental trip. The loop-spring 25 which is shown in FIG. 1 has the intended function of urging the lever 22 in the anticlockwise direction and thus removes this danger. In

consequence, the apparatus can have optimum sensitivity as a function of the maximum permissible im pact.

What I claim is:

1. In a single-pole circuit-breaker switch for manual operation and free tripping of the type comprising an insulating casing, two stationary contacts disposed in said casing, a hand-operated closure push-button slidably fitted within said casing and projecting therefrom, means for retaining said push-button in a depressed position, two movable contact means cooperating with said stationary contacts, and connected one to the other through the two arms of a U-shaped thermostatic element means, and elastic restoring means for returning the movable parts in the opening position at the time of operation of releasing means controlled by said thermostatic element, the improvement which consists in that said movable contact metrical right-angle brackets of cut-out and folded sheet metal to form flanges, said brackets being disposed in'the fon'n of a T and assembled by means of two spacer members; one of the spacer members being provided with a central internally threaded bore oriented in the axial direction, a lug means which is formed on each flange-of the right-angle brackets and adapted to engage in said axial groove of a corresponding half-casing for vertically guiding the assembled frame; an operating arm comprising two superposed side-plates disposed on each side of said operating blade and respectively joined together at upper and lower ends thereof by means of an upper and lower cross pin, said upper cross pin defining a retaining pin a and being engaged in said inclined groove of. said operating blace whereby axial 'force exerted on the blade applies a radial force component to said upper cross-pin, and wherein the extremities of said lower cross-pin are engaged in a double-slope groove provided in each bracket of the movable frame, saidlower cross-pin defining an actuating pin; an insulating guide for the retaining pin and a retaining plate means which are juxtaposed and stationarily fixed beneath the guide sleeve and forming an assembly having a central opening of dimensions permitting thepassage of the operating blade'and operating arm and preventing the passage of the retaining pin, a ramp disposed on each side of the means are carried by a frame slidably moving within said casing, said frame being linked to said push-button through a pivoting connection member, said frame being lockable by a lock acting on said connection member during the time of depression of said push-button, vsaid thermostatic element contacting a pivoting lever arranged so as to release saidlock at the time of deformation of the said thermostatic element and allow said sliding frame to move under the action of said restoring means.

2. A circuit-breaker switch according to claim 6, wherein said insulating casing comprises two identical hollowed-out shells having an axial and a lower groove, and wherein said two stationary contacts respectively engage in said lower groove of the casing shells, an insulating positioning unit for maintaining said contacts in spaced relation; a guide sleeve rigidly fixed to a top portion of the casing and having a threaded portion thereon whereby the apparatus can be attached to a panel by means of a nut; said control push-button being formed of three assembled insulating components which are at least partially housed and guided within said guide sleeve; an operating blade attached to and extending below the base of the control push-button, said blade having an inclined groove in the lower portion thereof; said movable frame comprising two symopining and terminating -in a recess, wherein said locking means comprises a latch pivotally disposed about-a pin carried by the brackets of the movable frame, said latch being provided on one side of said pin with a bearing nose and on the other side of said pin with a heel-shaped projection means for retaining said actuating pin and a finger means for replacing the latch in a normal position, a trip lever means pivotally mounted on a further pin carried by the brackets of the movable frame and provided with a heel an insulating stud forming part of said thermostatic element and loop spring means for urging said heel against said stud for determining as a function of current intensity which passes through the element the angular position of a retaining nose which cooperates with said bearing nose of said latch; an insulating contact-holder, means for positioning said contact-holder including a base member housed within a recess formed in the brackets of the movable frame and side-plates of said contactholder applied against external faces of said brackets;

an assembly plate for securing the contact-holder, said assembly plate carrying two projecting lug means for engagement in the axial guiding grooves of the casing; two movable and flexible S-shaped contact-holder strips centrally attached to the side plates of the insulating contact-holder and cooperating with the stationary contacts; said thermostatic element being constituted by a U-shaped bimetallic strip surrounding the movable frame for producing action on the heel of the trip lever, wherein the two arms of the U are respectively joined to upper extremities of the flexible strips for providing a direct electric circuit; an element means for providing compensation for ambient temperature constituted by two identical bimetallic strips having a double elbow with one extremity of each strip being clamped at a point of assembly of said thermostatic element and flexible strips and with the other extremity being mechanically clamped between two small insulating plates for producing action on the thermostatic ele- 3. A single-pole circuit-breaker switch according to claim 5, wherein the force which is applied at the point of contact between the nose of the latch and the nose of the trip lever is directed towards the pin on which the trip lever is pivotally mounted and wherein the distance between the point of engagement and the pivotal axis of the latch is equal at the maximum to the distance between the said axis and the point at which the reaction is applied between the actuating pin and the retaining heel.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,686,602 Dated August 22, 1972 Inventor(s) I Jean Jullien-Davin It is certified that error appears in the above-identified patent and that said 'Letters Patent are hereby corrected as shown below:

i [30] Foreign Application Priority Data Nov. 20, 1969 France.....69 40323 Signed and sealed this 9th day of January 1973.

- (SEAL) Attest:

ROBERT GOTTSCHALK Attesting Officer ORM po'wso uscoMM-Dc scam-P69 a U S. GOVERNMENY PRINTING OFFICE: 1559 0-35533 UNITED STATES PATENT OFFIQE CERTIFICATE GE GQRRECTWN Patent No. 3,686,602 Dated August 22, 1972 Inventor(s) Jean Jullien-Davin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[30] Foreign Application Priority Data Nov. 20, 1969 France.....69 40323 Signed and sealed this 9th day of January 1973.,

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents RM PO105O (10439) 

1. In a single-pole circuit-breaker switch for manual operation and free tripping of the type comprising an insulating casing, two stationary contacts disposed in said casing, a hand-operated closure push-button slidably fitted within said casing and projecting therefrom, means for retaining said push-button in a depressed position, two movable contact means co-operating with said stationary contacts, and connected one to the other through the two arms of a U-shaped thermostatic element means, and elastic restoring means for returning the movable parts in the opening position at the time of operation of releasing means controlled by said thermostatic element, the improvement which consists in that said movable contact means are carried by a frame slidably moving within said casing, said frame being linked to said push-button through a pivoting connection member, said frame being lockable by a lock acting on said connection member during the time of depression of said push-button, said thermostatic element contacting a pivoting lever arranged so as to release said lock at the time of deformation of the said thermostatic element and allow said sliding frame to move under the action of said restoring means.
 2. A circuit-breaker switch according to claim 6, wherein said insulating casing comprises two identical hollowed-out shells having an axial and a lower groove, and wherein said two stationary contacts respectively engage in saiD lower groove of the casing shells, an insulating positioning unit for maintaining said contacts in spaced relation; a guide sleeve rigidly fixed to a top portion of the casing and having a threaded portion thereon whereby the apparatus can be attached to a panel by means of a nut; said control push-button being formed of three assembled insulating components which are at least partially housed and guided within said guide sleeve; an operating blade attached to and extending below the base of the control push-button, said blade having an inclined groove in the lower portion thereof; said movable frame comprising two symmetrical right-angle brackets of cut-out and folded sheet metal to form flanges, said brackets being disposed in the form of a T and assembled by means of two spacer members, one of the spacer members being provided with a central internally threaded bore oriented in the axial direction, a lug means which is formed on each flange of the right-angle brackets and adapted to engage in said axial groove of a corresponding half-casing for vertically guiding the assembled frame; an operating arm comprising two superposed side-plates disposed on each side of said operating blade and respectively joined together at upper and lower ends thereof by means of an upper and lower cross pin, said upper cross pin defining a retaining pin and being engaged in said inclined groove of said operating blace whereby axial force exerted on the blade applies a radial force component to said upper cross-pin, and wherein the extremities of said lower cross-pin are engaged in a double-slope groove provided in each bracket of the movable frame, said lower cross-pin defining an actuating pin; an insulating guide for the retaining pin and a retaining plate means which are juxtaposed and stationarily fixed beneath the guide sleeve and forming an assembly having a central opening of dimensions permitting the passage of the operating blade and operating arm and preventing the passage of the retaining pin, a ramp disposed on each side of the opining and terminating in a recess, wherein said locking means comprises a latch pivotally disposed about a pin carried by the brackets of the movable frame, said latch being provided on one side of said pin with a bearing nose and on the other side of said pin with a heel-shaped projection means for retaining said actuating pin and a finger means for replacing the latch in a normal position, a trip lever means pivotally mounted on a further pin carried by the brackets of the movable frame and provided with a heel an insulating stud forming part of said thermostatic element and loop-spring means for urging said heel against said stud for determining as a function of current intensity which passes through the element the angular position of a retaining nose which cooperates with said bearing nose of said latch; an insulating contact-holder, means for positioning said contact-holder including a base member housed within a recess formed in the brackets of the movable frame and side-plates of said contact-holder applied against external faces of said brackets; an assembly plate for securing the contact-holder, said assembly plate carrying two projecting lug means for engagement in the axial guiding grooves of the casing; two movable and flexible S-shaped contact-holder strips centrally attached to the side plates of the insulating contact-holder and cooperating with the stationary contacts; said thermostatic element being constituted by a U-shaped bimetallic strip surrounding the movable frame for producing action on the heel of the trip lever, wherein the two arms of the U are respectively joined to upper extremities of the flexible strips for providing a direct electric circuit; an element means for providing compensation for ambient temperature constituted by two identical bimetallic strips having a double elbow with one extremity of each strip being clamped at a point of assembly of said thermostatic element and flexible strips and with the other extremIty being mechanically clamped between two small insulating plates for producing action on the thermostatic element; an adjusting screw means carried by the movable frame for bringing the thermostatic element into a position corresponding to a calibration value; a blade-spring means for maintaining the assembly plate on the movable frame and for permitting oscillation and axial displacement of the compensating element; and wherein said restoring means includes a compression spring housed within an axial bore formed in the stationary-contact positioning unit for reacting with the assembly plate and thrusting back the movable frame towards the top of the casing.
 3. A single-pole circuit-breaker switch according to claim 5, wherein the force which is applied at the point of contact between the nose of the latch and the nose of the trip lever is directed towards the pin on which the trip lever is pivotally mounted and wherein the distance between the point of engagement and the pivotal axis of the latch is equal at the maximum to the distance between the said axis and the point at which the reaction is applied between the actuating pin and the retaining heel. 